How to diagnose and fix overlocker tension issues

If your overlocker stitches don’t look quite right, you’re not alone. Tension issues are one of the most common reasons sewists feel frustrated or nervous about using an overlocker. The good news? Once you understand how the stitches are formed and how the threads work together, diagnosing and fixing overlocker tension problems becomes much simpler than it first appears.

In this guide, I’ll walk you through how to identify exactly which thread is causing the issue and what to adjust, so you can spend less time troubleshooting and more time enjoying your sewing.

Whether you’re brand new to overlocking or just want to feel more confident with your machine, this is one of those skills that pays off again and again.

Why overlocker tension feels intimidating (and why it shouldn’t)

The word overlocker (or serger if you’re in the US) has a reputation for striking fear into the hearts of many sewists. Lots of threads, lots of dials and very little confidence that you’re doing it right.

But here’s the truth: overlockers aren’t complicated machines. They’re just misunderstood.

Once you know:

• what each thread does
• where it should appear in a balanced stitch
• and how tightening or loosening tension affects the stitch

…you can troubleshoot most issues quickly and calmly.

And it’s absolutely worth learning. A well-set overlocker gives your projects a professional finish and is brilliant for sewing knit and jersey garments.

The two main causes of overlocker problems

Almost every overlocker issue comes down to one of two things:

1. Incorrect threading
2. Incorrect tension

Before touching a single tension dial, always start with threading.

Step one: check your overlocker is threaded correctly

Correct threading is crucial. Even a tiny mistake can cause tension problems that no amount of dial-twiddling will fix.

If you’re unsure, rethread the machine from scratch rather than trying to fix things halfway through.

Top threading tips

• Always thread with the presser foot up
  This opens the tension discs so the thread can seat properly. If the foot is down, the thread won’t enter the discs and tension issues are guaranteed.
• Thread in four different colours
  This makes it much easier to see which thread is misbehaving.
• Follow the correct threading order
  Your machine manual (or a step-by-step video) is your best friend here.

On our website, you’ll find detailed threading tutorials for many machines, including manual threading and air-threading overlockers. We also have our video 'How to Thread an Overlocker' featuring Brother overlockers.

Understanding overlocker anatomy (in simple terms)

Most overlockers work in the same way, regardless of brand. They use four threads:

• Upper looper
• Lower looper
• Right needle
• Left needle

Each thread has its own tension dial. On many machines, including the Brother 3034D, the dials are numbered, with a mid-range setting (often between 3 and 5) suitable for most fabrics.

If a thread is:

• too loose → increase the tension (turn the number up)
• too tight → decrease the tension (turn the number down)

Some machines, such as most of the Baby Lock overlocker range, handle this automatically. If you want maximum ease and minimal setup, those models are well worth exploring.

Not only do they have automatic thread tension, they are also incredibly easy to thread thanks to something called air threading, which threads the loopers at the touch of a lever/button.

What a balanced overlocker stitch should look like

Before diagnosing problems, it helps to know what you’re aiming for.

On a balanced stitch:

• The needle threads run in neat, parallel lines on the right side
• The upper looper weaves neatly between those needle stitches
• On the wrong side, you see only the lower looper thread
• On the right side, you see only the upper looper thread
• The stitches sit right on the fabric edge, without hanging over or pulling in

Once you’ve seen and felt a balanced stitch, spotting issues becomes much easier.

Diagnosing common overlocker tension problems

Lower looper tension issues

Lower looper too tight

• Upper looper thread is pulled onto the wrong side
• Lower looper thread is barely visible underneath
• Fabric may feel slightly tunnelled

Fix: Reduce the lower looper tension.

Lower looper too loose

• Lower looper thread appears on the right side
• Stitch looks messy and unbalanced

Fix: Increase the lower looper tension.

Upper looper tension issues

Upper looper too loose

• Upper looper thread appears on the wrong side
• Stitch lacks definition

Fix: Increase the upper looper tension.

Upper looper too tight

• Lower looper thread is pulled onto the right side
• Fabric may appear compressed

Fix: Reduce the upper looper tension.

Needle tension issues

Right needle too tight

• Fabric is compressed or concertinaed
• Loopers look distorted on the right side

Fix: Reduce right needle tension.

Right needle too loose

• Stitch looks like a single long line
• Needle thread loops on the wrong side

Fix: Increase right needle tension.

Left needle too tight

• Stitch looks dense with no definition
• Fabric appears pulled in

Fix: Reduce left needle tension.

Left needle too loose

• Left needle stitch is pulled across by the right needle
• Loops appear on the wrong side

Fix: Increase left needle tension.

A confidence-boosting tip that makes all the difference

One of the biggest causes of overlocker frustration is trying to troubleshoot while you’re in the middle of a project.

Instead, set aside an hour purely to:

• thread your machine
• sew test samples
• deliberately adjust tensions
• and observe what changes

Create your own reference samples and keep them nearby. When something looks off in the future, you’ll instantly recognise what’s happening and know exactly what to adjust.

That small investment of time pays back every time you sit down to sew.

Want more help with your overlocker?

There are lots of step-by-step overlocker tutorials, tips and project videos on our YouTube channel, including guides on getting the best results from your machine and sewing garments entirely on an overlocker.

We release new videos every week, packed with practical advice and inspiration. You can also sign up to our newsletter for tutorials, product guides and sewing ideas delivered straight to your inbox.

And if you ever need personalised advice, whether you’re choosing an overlocker or getting to grips with one you already own, our team is always happy to help.

Happy sewing, and enjoy getting confident with your overlocker.